1. Field of the Invention
This invention relates to vent systems for fuel-burning appliances and, more particularly, to a direct vent system that communicates between an internal space, within which the appliance is located, and the external atmosphere, through a vertically extending sidewall.
2. Background Art
Fuel-burning appliances are commonly equipped with direct sidewall vent systems. Typically, concentric conduits communicate between the appliance and an external atmosphere generally in a horizontal direction through an outside, vertically extending sidewall. An inner conduit communicates combustion gases from the appliance to the external atmosphere. An annular passage between the inner conduit and a surrounding conduit communicates makeup air from the external atmosphere to the appliance.
Ideally, to optimize operation and efficiency of the fuel-burning appliance, air flow volume to, and pressure in, the appliance burner are maintained within specific ranges. Reduced air flow to the burner may cause sooting, which is detrimental to the appliance and also produces pollutants that are undesirably discharged to the atmosphere and potentially to against the interior and exterior of the building within which the appliance is located.
The type and location of the intake for makeup air and its relationship to the subjacent surface, combustion gas outlet, and wall upon which the vent system is mounted, are critical in the design of such systems to maintain adequate air flow. Myriad different makeup air intakes have been devised in the industry. It is known, for example, to provide a makeup air intake at one side, or opposite sides, of the conduits. Operation of certain of these systems may be adversely affected by atmospheric wind conditions.
Environmental winds may adversely affect other vent designs as well. High winds tend to block the discharge of combustion gas. A pressure buildup may result in the combustion chamber that slows down air flow to the burner. This may result in sooting, with the attendant disadvantages, noted above.
More commonly, the makeup air is drawn from a region at the bottom of the external portion of the vent system. These bottom located intakes have some of their own inherent disadvantages.
Commonly, those installing direct vent systems will locate the external portion of the vent system in close proximity to the ground, either at the behest of the building owner, for purposes of aesthetics, or for reasons dictated by the building geometry or convenience and ease of installation. Manufacturers of these vent systems typically will specify a minimum clearance between the external portion of the vent system and the subjacent ground. Even within these specifications, there are some inherent problems that are commonly encountered.
First of all, an accumulation of snow or debris may effectively reduce the clearance between the makeup air intake and the ground. The intake may be partially, or in a worse case altogether, blocked so that the required air flow does not occur at the combustion chamber.
Even if the clearance is within manufacturers' specifications, there is also the possibility that atmospheric winds may interact with the ground and surrounding structures to produce undesired pressure buildup at the makeup air intake.
Further, the discharged gases, and potentially pollutants, entrained therein, may be redirected at the subjacent surface so as to be recirculated by being drawn back into the makeup air intake. At low mounting heights, the makeup air intake is also prone to picking up debris that may be elevated thereto by winds and/or the discharging combustion gases. This debris may be detrimentally recirculated to the appliance.
Heretofore, in the interest of facilitating installation, or addressing aesthetic concerns, building owners have mounted the external vent components in close proximity to the ground, which has caused them to have to contend with the above-mentioned problems associated with conventional vent systems; notably variations in efficiency of the appliance operation, temporary flame-outs, sooting, etc. The industry continues to seek out designs to address some or all of the above problems.